This invention relates to a position sensor and in particular to a sensor of the type that senses the relative longitudinal displacement of two members by applying a signal to a sensor probe and measuring an electrical parameter that varies in proportion to the relative displacement of two portions of the probe.
Automotive ride control systems provide active suspension response to road conditions by reacting to forces tending to compress the suspension members. In order to accomplish this, it is necessary to provide a real time measurement of the position of various portions of the suspension system, such as each wheel assembly, with respect to the vehicle frame. Those relative position variables are provided as an input to a ride control computer, which dynamically responds by adjusting the fluid pressure in the respective shock absorbers.
One preferred location for such a position sensor is internal to the associated shock absorber, where the movement of each wheel assembly may be monitored by the relative movement of the telescoping shock absorber members. The environment internal to a shock absorber is extremely hostile, subjecting an internally mounted sensor to pressures of up to 6500 psi and temperatures of up to 135.degree. C. Accordingly, a linear position sensor located internal to a shock absorber must be compact and extremely rugged and durable in nature. Even when located external of the shock absorber, such a position sensor used with an automotive ride control system will be exposed to a severe environment which requires that the sensor be resistant to degradation by various automotive fluids and be extremely stable under wide swings in ambient temperature. Additionally, to be successful in the automotive field, such a position sensor must necessarily be inexpensive to produce, be reliable in performance and experience very little wear over extended periods.